I don't normally use the term "negative" when referring to a layout. I tend to think of them in terms of pin distance from the axis, pin distance from the val (vertical axis line) and MB distance from axis (assumed mb on symmetric core balls), or Mo Pinel's degree system.
With that being said, I do not use any ball with the pin closer than 5" to my axis. I am rev dominant. With my coordinates of 5 1/8x0, some of my layouts end up with the pin on the track side of the midline. With a symmetric core, the longer pin distance cuts the flare and gives me length, on asyms length with flare and the hook shape dictated by mb placement. I use pin distances up to 6 1/4" from the axis. At that distance on symmetric I get length and control. Any further than 6 1/4" away and you risk reverse flaring on an errant shot. As to which ball to choose, it depends on exactly what I am trying to accomplish. I have a Roto Grip Riot drilled 50x6"x70 (pin under and just left of mf) which gives me alot of length and control, and a 2Furious 60x6"x55 (pin in mf) which gives me a conservative ball to use on patterns on the longer side. I also have an Anarchy 6" pin to pap, 3" pin to val 3.5" mb to axis, (pin over mf) which gives me a strong skid/flip.
Hope this helps you
